The present invention relates to a keyboard connection apparatus and a keyboard input apparatus for an information processing system such as a personal computer.
2. Description of the Related Art
Generally, in an information processing system such as a personal computer, besides a system keyboard, an additional keyboard can be connected.
When the additional keyboard is not connected, an input signal from the system keyboard is outputted. In contrast, when the additional keyboard is connected, the input signal from the additional keyboard is outputted in a higher priority than that from the system keyboard. In such a conventional keyboard input apparatus, the additional keyboard is connected by using a connector with a switch. The system keyboard is connected to a CPU (Central Processing Unit) through a connection circuit, and the additional keyboard can be connected to the connector with the switch. When a control signal to be input to the control circuit goes low, the input signal is passed therethrough. However, when the control signal goes high, the impedance of the output terminal of the connection circuit becomes high causing the input signal to cutoff.
When the additional keyboard is not connected to the connector with the switch, the switch of the connector causes a low voltage control signal to be applied to the control signal input terminal of the connection circuit. Thus, in this state, the connection circuit is turned on and thereby the output signal from the system keyboard is inputted to the CPU through the connection circuit.
When the additional keyboard is connected to the connector with the switch, the switch of the connector causes a high voltage control signal to be applied to the control signal input terminal of the connection circuit. Thus, in this state, the impedance of the connection circuit becomes high and thereby the output signal from the system keyboard is cutoff and the output signal from the additional keyboard is inputted to the CPU through the connector with the switch.
In the aforementioned keyboard connection apparatus, the additional keyboard should be connected by using the connector with the switch. Since the connector with the switch is large in size, the entire system proportionally becomes large.
Moreover, since the connector comes with the switch, the composition of the connector becomes more complicated and expensive than that with no switch.